The traditional method of obtaining a fingerprint image is to first apply ink to a subject's finger, and then to transfer the fingerprint pattern of ridges and valleys to a piece of paper by pressing the finger to the paper. The fingerprint pattern of ridges transfers to the paper, while the valleys do not. To obtain a rolled fingerprint image, a side of an inked finger is placed in a designated area of the paper and then the finger is rolled to its other side on the paper.
Opto-electronic systems can capture a rolled fingerprint image without the use of ink. Typically, a series of optical images of a rolling finger on an imaging surface are propagated from an image sensor and converted to digital data. A variety of methods can be used to generate a rolled fingerprint image from the digital data representative of the series of images.
The drive toward increased optical resolution is seen across the fingerprint imaging industry. The increase in image sensor resolution in recent years clearly indicates this industry trend.